This invention relates to a rotating magnetic head suitable for use with a rotary head drum of a high density magnetic recording and/or reproduction apparatus of the helical scanning type such as a video tape recorder (VTR) or a tape streamer, and more particularly to a technical field which relates to the shape of a head chip for a magnetic head.
Conventionally, in a plurality of rotating magnetic heads incorporated in a rotary head drum of a VTR, a tape stream or the like, a magnetic gap in the form of a slit having a width equal to the width of a signal recording track is formed at a substantially center of a tape sliding surface, which contacts with a magnetic tape, at an end of a head chip formed from a magnetic core.
The head chip helically scans the magnetic tape at a high speed to record or reproduce (write or read) a signal (data) onto or from the magnetic tape through magnetism conversion at the gap thereof.
FIGS. 12 and 13 show a rotary head drum 1 of a high density recording and reproduction apparatus of the helical scanning type of a conventional VTR, tape streamer or like apparatus. Referring to FIGS. 12 and 13, the rotary head drum 1 shown includes a plurality of rotating magnetic heads 6 including a plurality of recording heads 4 and a plurality of reproduction heads 5 mounted radially by means of screws 7 on and along an outer circumference of a lower end edge of a rotary drum 3 which is rotated above a fixed drum 2.
Each of the rotating magnetic heads 6 has a head chip 11 securely mounted at a radially outer end thereof. When the rotary drum 3 is rotated at a high speed in a direction indicated by an arrow mark b while a magnetic tape 21 is helically wrapped on an outer periphery of the rotary head drum 1 along a tape lead 8, which is a stepped portion formed helically on an outer circumference of the fixed drum 2, and is fed at a constant speed in a direction indicated by an arrow mark a, the magnetic tape 21 is helically scanned by the head chips 11 of the rotating magnetic heads 6 so that helical, high density recording or reproduction of signals (data) onto or from the magnetic tape 21 is performed.
Referring now to FIGS. 14, 15A and 15B, each of the head chips 11 has a tape sliding surface 12 and a magnetic gap 13 formed at a radially outer end thereof. The tape sliding surface 12 is formed in a substantially arcuate shape along two directions including the rotation direction b and a direction perpendicular to the rotation direction b, and the magnetic gap 13 is formed at a substantially central portion of the tape sliding surface 12 in the rotation direction b. A pair of upper and lower grooves 14 and 15 for permitting escapement of air therethrough are formed in parallel to the direction of the arrow mark b on the opposite upper and lower sides of the magnetic gap 13. The head chip 11 thus records (writes) or reproduces (reads) a signal at a high density onto or from a signal recording surface 21a of the magnetic tape 21 through electromagnetism conversion at the magnetic gap 13. In particular, upon signal recording, an electric signal is converted into magnetic fluxes, but upon reproduction, such a magnetic signal is converted into an electric signal.
More particularly, referring to FIG. 16, upon signal recording, the signal recording surface 21a of the magnetic tape 21 which is fed at a constant speed in a direction of an arrow mark a is helically scanned at a high speed in a direction of an arrow mark b from a lower edge 21b toward an upper edge 21c of the magnetic tape 21 by the head chips 11 of the plurality of recording heads 4 to successively record belt-like signal tracks (belt-like signal recording patterns) TR1, TR2, TR3, TR4, . . . , TRn at a fixed track pitch P onto the signal recording surface 21a of the magnetic tape 21 by means of the magnetic gaps 13 of the head chips 11. On the other hand, upon signal reproduction, the signal tracks TR1, TR2, TR3, TR4, . . . , TRn of the magnetic tape 21 are helically scanned in the direction of the arrow mark b successively by the head chips 11 of the plurality of reproduction heads 5 similarly as upon recording to successively reproduce the signal tracks TR1, TR2, TR3, TR4, . . . , TRn.
In order to achieve higher density recording for allowing recording and reproduction for a longer period of time while decreasing the consumed amount of magnetic tapes in the magnet recording and reproduction apparatus of the helical scanning type which uses a magnetic tape as described above, two countermeasures are available including a countermeasure of decreasing the track width of the signal tracks TR to be recorded onto the magnetic tape 21 and another countermeasure of decreasing the wavelength of a signal to be recorded. However, whichever one of the countermeasures is adopted, a drop of the head output cannot be avoided.
On the other hand, it seems a possible idea to decrease the depth of the magnetic gap 13 of the rotating magnetic head 6 to increase the head output. However, if the depth of the magnetic gap 13 is decreased, then even if the abrasion amount of the head per unit time is equal, the magnetic gap 13 opens in shorter time. Consequently, replacement of the rotating magnetic head 6 after a shorter interval of time is required, and a rise of the maintenance cost cannot be avoided.
In order to reduce the abrasion of the head, it seems a possible idea to increase the head contacting width over which the tape sliding surface 12 of each of the head chips 11 of the rotating magnetic head 6 contacts with the magnetic tape 21 to decrease the contacting pressure of the magnetic tape 21 with the tape sliding surface 12. It is to be noted that increase of the head contacting width decreases the abrasion of the magnetic gap 13.
Incidentally, the most significant factor of the head abrasion is a great number of very small magnetic particles of approximately several tens nm and so forth which naturally stick to the signal recording surface 21a of the magnetic tape 21 in a manufacturing process of the magnetic tape 21, and when the head chip 11 of the rotating magnetic head 6 helically scans the signal recording surface 21a of the magnetic tape 21, the tape sliding surface 12 of the head chip 11 is abraded by grinding force of the very small magnetic particles and so forth.
Particularly, when a fresh portion of the signal recording surface 21a of a new magnetic tape 21 on which no signal track TR is written as yet is helically scanned for the first time by a head chip 11, the head abrasion amount by the grinding force of the very small magnetic particles and so forth is naturally greater than that when an old portion of the signal recording surface 21a on which signal tracks TR are written already is helically scanned.
The reason why the head abrasion amount can be reduced by increasing the head contacting width of a head chip 11 is described with reference to FIGS. 15A, 15B and 17.
FIG. 15A shows a head chip 11S which is a conventional popular head chip wherein the head contacting width W1 of the tape sliding surface 12 is small while FIG. 15B shows a head chip 11L wherein the head contacting width W2 of the tape sliding surface 12 is increased uniformly in upward and downward directions.
FIG. 17A illustrates a manner wherein the “head 1”, “head 2”, “head 3” and “head 4” each including the head chip 11S having the tape sliding surface 12 of the small head contacting width W1 successively helically scan the signal recording surface 21a of the magnetic tape 21, which is fed at a constant speed in the direction of the arrow mark a, in order at a high speed in the direction of the arrow mark b at a fixed track pitch P.
Meanwhile, FIG. 17B illustrates a manner wherein the “head 1”, “head 2”, “head 3” and “head 4” each including the head chip 11L having the tape sliding surface 12 of the great head contacting width W2 successively helically scan the signal recording surface 21a of the magnetic tape 21, which is fed at a constant speed in the direction of the arrow mark a, in order at a high speed in the direction of the arrow mark b at a fixed track pitch P.
Since, in order to increase the recording density, it is necessary to decrease the width W3 of the magnetic gaps 13 of the head chips 11S and 11L which corresponds to the track width of the signal tracks TR to be recorded onto the magnetic tape 21, the head contacting width W1 or W2 is inevitably greater than the width W3 of the magnetic gap 13.
Accordingly, whichever one of the head chips 11S and 11L is used, when the tape sliding surfaces 12 of the “head 1”, “head 2”, “head 3” and “head 4” successively helically run (slidably move) on the signal recording surface 21a of the magnetic tape 21 in order at a fixed track pitch P, a lower side portion of a run portion (running locus) of the signal recording surface 21a along which the tape sliding surface 12 of each head runs with the head contacting width W1 or W2 overlaps with an upper side portion of a run portion (running locus) of the signal recording surface 21a along which the tape sliding surface 12 of a preceding head runs with the head contacting width W1 or W2.
In FIG. 17A, an overlap portion of a run portion by a succeeding head with a run portion by a preceding head among the “head 1”, “head 2”, “head 3” and “head 4” which each includes the head chip 11S of the small head contacting width W1 is indicated as “twice run portion”.
In particular, in the case described above, a lower side portion of a run portion by a succeeding head overlaps, only once at a portion indicated as “twice run portion”, with an upper side portion of a run portion of a preceding head and besides over a comparatively small overlap width. Accordingly, in each “once run portion” which does not overlap with another run portion and has a comparatively great width, a head runs on a normally new portion of the signal recording surface 21a of the magnetic tape 21 on which no preceding head has run (slidably moved). Also the magnetic gap 13 of a succeeding head always runs on a new portion of the signal recording surface 21a of the magnetic tape 21 on which no preceding head has run (slidably moved).
Meanwhile, in FIG. 17B, overlap portions of a run portion by succeeding heads with a run portion by a preceding head among the “head 1”, “head 2”, “head 3” and “head 4” which each includes the head chip 11L of the great head contacting width W2 are indicated as “twice run portion” and “three-time run portion”.
In particular, in the case just described, a lower side portion of a run portion by a succeeding head overlaps, twice at portions indicated as “twice run portion” and “three-time run portion”, with upper side portions of run portions by two preceding heads. Thus, in each comparatively great width run portion w1 indicated as “run portion W1 preceding to head gap”, the magnetic gap 13 can run on an old portion of the signal recording surface 21a of the magnetic tape 21 on which a preceding head or heads have run (slidably moved).
From the foregoing, it can be recognized that the abrasion amounts at the tape sliding surface 12 and the magnetic gap 13 of the head chip 11 by grinding force of very small magnetic particles and so forth sticking to the signal recording surface 21a of the magnetic tape 21 described hereinabove can be reduced with the head chip 11L which has the greater head contacting width W2 when compared with the head chip 11S which has the smaller head contacting width W1.
However, if the head contacting width W2 of the tape sliding surface 12 of the head chip 11 is merely increased as seen in FIG. 15B, then since the amount of air drawn in between the tape sliding surface 12 and the magnetic tape 21 increases, the spacing or distance between the head chip 11 and the magnetic tape 21 increases, resulting in decrease of the head output.
Therefore, it is demanded to decrease the abrasion of the head chip 11 by grinding force of very small magnetic particles and so forth while sufficient contact between the head and the tape is secured.
Therefore, in order to secure sufficient contact between the head and the tape, it has been conventionally proposed to form, as described hereinabove with reference to FIGS. 14, 15A and 15B, a pair of upper and lower grooves 14 and 15 on the opposite upper and lower sides of the magnetic gap 13 in an upwardly and downwardly symmetrical relationship on the tape sliding surface 12 such that they extend in parallel to the direction of rotation of the head so that, upon helical scanning of the magnetic tape 21 by the head chip 11, the magnetic tape 21 may be attracted to the tape sliding surface 12 of the head chip 11 by a negative pressure effect by an air escaping action in the pair of upper and lower grooves 14 and 15, as disclosed in Japanese Patent Laid-Open Nos. Hei 1-151019, Hei 1-235012, Hei 2-240806 and Hei 11-316904.
However, even if the countermeasure described is adopted, if the head contacting width of the tape sliding surface 12 of the head chip 11 is increased in an upwardly and downwardly symmetrical relationship as seen in FIG. 15B, then this likewise gives rise to a problem that the spacing between the head chip 11 and the magnetic tape 21 increases. Therefore, the countermeasure still has a limitation to increase of the head contacting width while securing the head output.
On the other hand, in order to reduce the head abrasion, another countermeasure has been proposed wherein a plurality of dummy heads are disposed at preceding positions to the plurality of rotating magnetic heads 6 of the rotary head drum 1 such that the dummy heads grind very small magnetic particles and so forth sticking to the signal recording surface 21a of the magnetic tape 21 earlier than the rotating magnetic heads 6 while the rotating magnetic heads 6 helically scan the signal recording surface 21a of the magnetic tape 21.
Where the dummy heads are used in this manner, since the head grinding force by very small magnetic particles and so forth on the magnetic tape 21 decreases in proportion to the number of times by which a head runs on the magnetic tape 21 as seen from a graph of FIG. 18, the life of the head can be increased.
However, where a plurality of dummy heads are mounted on the rotary head drum 1 in this manner, this gives rise to another problem that a rise in cost cannot be avoided, and besides, also the maintenance cost increases because it is necessary to replace the dummy heads when they are abraded.
Further, since a pair of grooves on a head chip are formed in parallel to the direction of rotation of the head chip, if foreign substances such as magnetic particles sticking to the surface of the magnetic tape are transferred and stick now between the pair of grooves on the tape sliding surface of the head chip on the leading side in the direction of rotation of the head chip with respect to the magnetic gap, then the foreign substances such as the magnetic particles are carried, as the head chip rotates, in a direction parallel to the direction of rotation of the head chip on the tape sliding surface until they come to and are accumulated in the magnetic gap thereby to frequently cause clogging of the magnetic gap.
Accordingly, only if a pair of grooves are formed on the opposite sides of the magnetic gap on the tape sliding surface of the head chip such that they extend in parallel to the direction of rotation of the head chip, it is not easy to solve the problem of the spacing loss by clogging of the magnetic gap.